Photographic emulsions containing metallic mercury



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Stats PHOTOGRAPHIC EMULSIONS CONTAINING METALLIC MERCURY No Drawing. Application November 24, 1953, Serial No. 394,215

Claims. (Cl. 96-108) This invention relates to fog inhibiting agents and stabilizers for photographic emulsions and to photographic emulsions containing them.

It is well known that photographic emulsions on storage tend to lose sensitivity and to become spontaneously developable without exposure to light. There is normally a detectable amount of the silver salt reduced during development in the areas where no exposure was given; this is commonly called fog, and sometimes called chemical fog where it is necessary to distinguish between-it and theefliects of accidental exposure to radiation; in this invention, we are not concerned with the latter.

Fog depends both on the emulsion and the conditions of development; for a given emulsion it increases with the egree of development. With constant development conditions, it tends to increase with time, temperature and relative humidity of storage conditions; it is common practice to make accelerated tests of the stability of photographic emulsions by storage at increased temperature or humidity, or both. It is, of course, desirable to have emulsions as stable as possible under the conditions of high temperature and humidity which may occur in tropical climates, for example. Fog usually appears over the Whole area of the sensitive coating, but when severe, it frequently is non-uniform. Fog may also be caused by exposure to chemicals, for example, hydrogen sulfide and other reactive sulfur compounds, hydrogen peroxide vapor, and strongly reducing materials. While antifoggant's andstabilizers may protect, to some extent, against such effects, it is normally understood that an antifoggant protects against spontaneous growth of fog during prolonged storage or storage at high temperatures and humidities, or during development to maximum contrast and speed, or both.

It is an object of the invention to provide novel antifogging or fog inhibiting agents for emulsions. A further object is to provide antifogging agents which stabilize the initial sensitivity of the emulsion. A still further object is to provide antifogging agents which improve the keeping of the emulsion in tropical regions. Other objects will appear from the following description of my invention.

These objects are accomplished by incorporating in a silver halide emulsion a small amount of elemental mercury in the form of metallic mercury or mercury-gold amalgam.

it is known that mercury compounds can be added to silver halide emulsions in order to improve their stability and image-forming characteristics. The use of certain mercury compounds as antifoggants for silver halide emulsions is described in Allen, Byers, and Murray U. S. Patent 2,728,663, Carroll and Murray U. 5. Patent 2,728,664, and Leubner and Murray, U. S. Patent 2,728,665. The present invention distinguishes over all of these in that mercury is used in its elemental form and not in chemical combination With any other element.

The principal purpose of our invention is to provide a means for maintaining the sensitivity and fog of silver halide emulsions at or close to initial optimum values under keeping conditions of high temperature and humidity. The fog inhibitors which we propose to use are added to the emulsion at any stage during the process of manufacture prior to coating the emulsion to avoid loss of sensitivity and to inhibit the growth of incubation or keeping fog with passage of time under non-ideal conditions of storage. The mercury is added to the silver halide emulsion in dispersion in a water-permeable colloidal medium such as gelatin.

When the mercury is added in suitable concentration before coating to unsensitized or optically sensitized silver halide emulsions, it usually does not appreciably affect the sensitometric values for sensitivity and fog When measurements are made soon after coating. However, when sensitometric measurements are made after appreciable intervals of time under tropical or dry conditions of storage at elevated temperatures, the mercury or mercury amalgam does stabilize photographic speed and maintain fog at a low level.

The preparation of silver halide emulsions involves three separate operations: (1) the emulsification and digestion or ripening of the silver halide, (2) the freeing of the emulsion from aqueous soluble salts usually by Washing, (3) the second digestion or after-ripening to obtain increased sensitivity (Mees, The Theory of the Photographic Process, 1942, page 3). The mercury fog inhibiting agents may be added at any stage, e. g., after the final digestion.

Our fog inhibiting agents are useful generally in photographic silver halide developing-out emulsions. They may be used in emulsions chemically sensitized with sulfur compounds, reducing agents, or noble metals such as gold or by various combinations of these asdescribed more fully hereinafter.

The most useful concentration of fog inhibitor is from 0.01 to 3.0 mg. of fog inhibitor per mole of silver halide in the emulsion.

The emulsions may be chemically sensitized by any of the accepted procedures; for example, they may be digested with naturally active gelatin, or sulfur compounds may be added such as those described in Sheppard U. S. Patents 1,574,944 and 1,623,499, and Sheppard and Brigham U. S. Patent 2,410,689.

The emulsions may also be treated with salts of the noble metals such as ruthenium, rhodium, palladium, iridium and platinum, all of which belong to group VIll of the periodic table of elements and have an atomic weight greater than 100. Representative compounds are ammonium chloropalladate, potassium chloroplatinate and sodium chloropalladite, which are used for sensitizing in amounts below that which produces any substantial fog inhibition, as described in Smith and Trivelli U. S. Patent 2,448,060, and as antitoggants in higher amounts, as described in Trivelli and Smith U. S. Patents 2,566,245 and 2,566,263.

The emulsions may also be chemically sensitized with gold salts as described in Waller and Dodd U. S. Patent 2,399,083, Damschroder U. S. Patent 2,597,856, and Yutzy and Teermakers U. S. Patent 2,597,915. Suitable compounds are potassium chloroaurite, potassium aurithiocyanate, potassium chloroaurate, auric trichloride and Z-aurosulfobenzothiazole methochloride.

The emulsions may also be chemically sensitized with reducing agents such as stannous salts (Carroll U. S. Patent 2,487,850), polyamines such as diethylene triamine (Lowe and Jones U. 5. Patent 2,518,698), polyamines such as spermine (Lowe and Allen U. S. Patent 2,521,925), orbis-(fl-aminoethyl) sulfide and its watersoluble salts (Lowe and lones'U. S. Patent 2,521,926).

Dispersions of metallic mercury or mercury-gold amalgam were prepared as follows:

Example 1 A mercury dispersion was prepared as described by Treadwell and Hall in Analytical Chemistry, 6th edition, p. 214, .by first forming two solutions: (1) a solution made by dissolving grams of photographic gelatin in 50 cc. of water and then adding 0.0631 gram of potassium cyanide and (2) a solution made by dissolving 0.289 gram of HgNO -2H O in 25 cc. of 2% solution of perchloric acid. Solution (2) was added to solution (1) with strong stirring and allowed to set in a brine bath. The resulting dispersion was light gray in color and not transparent. The dispersion was broken into small pieces and washed in live changes of cold distilled water, three liters each. It was then melted and distilled water added to bring the total volume to 200 cc. The resulting dispersion contained 0.5 mg. per cc. of metallic mercury.

Example 2 A dispersion of mercury-gold amalgam, 50% gold and 50% mercury was made by first forming four solutions: (1) a solution made by dissolving 0.64 gram of Hg(NO -H O in 200 cc. of water, (2) a solution made by dissolving 0.756 gram of potassium chloroaurate in 200 cc. of water, (3) a solution made by dissolving one gram of sodium thiocyanate in 100 cc. of water, and (4) a solution made by dissolving 5 grams of photographic gelatin in 50 cc. of water and then adding 0.25 gram of hydrazine dihydrochloride. 25 cc. of solution (1) was mixed with 25 cc. of solution (2) and cc. of solution (3). The mixture was added to solution (4) and immediately 5 cc. of concentrated ammonium hydroxide solution were added. The mixture was allowed to stand in the refrigerator about 2 days and the dispersion was then broken into small pieces and washed in five changes of cold distilled water three liters each. It was then melted and distilled water was added to bring the total volume to 200 cc. The dispersion contained 0.5 mg. per cc. of amalgam.

Example 3 A dispersion of mercury-gold amalgam containing mercury and 80% gold (molar percentages) was made as in Example 2 except that 10 cc. of solution 1) were mixed with 40 cc. of solution (2) and 15 cc. of solution (3). The procedure was otherwise the same as Example 2 and a dispersion was obtained containing 0.5 mg. per cc. of the amalgam.

The following examples illustrate the preparation of silver halide emulsions containing mercury or mercurygold amalgam according to my invention. In testing these emulsions for the effect of moist or dry heat upon keeping, they were incubated under tropical conditions for fourteen days or at 120 F. dry heat for 7 days.

Example 4 A quantity of the mercury dispersion of Example 1 was added to a negative-speed gelatino-silver bromoiodide emulsion at a concentration of 0.1 mg. of mercury per mole of silver halide. The emulsion was coated on glass plates, dried, exposed on an Eastman IIb sensitometer and processed, before and after incubation as indicated in the table, for 5 minutes development in a developer of the following composition:

Gs. N-methyl-p-aminophenol sulfate 2.2 Hydroquinone 8.8 Sodium sulfite (desiccated) 96 Sodium carbonate (desiccated) 48 Potassium bromide 5 Water to 1 liter The following photographic results were obtained:

Speed Gamma Fog Control:

.00 .10 F. incubation 10 The emulsion containing the mercury-gold amalgam dispersion showed no speed loss on incubation and had a lower fog loss than the control.

Example 5 A quantity of the mercury-gold amalgam of Example 3 was added to a negative-speed gelatino-silver bromoiodide emulsion at a concentration of 2.5 mgs. of mercury-gold amalgam per mole of silver halide. The emulsion was coated on glass plates and treated as in Example 4. The following results were obtained:

Speed Gamma Fog Control:

Original n 1,900 1.25 .08 Tropical incubation .34 2.5 mg. mercury-gold amalgam per mole silver halide:

Original .09 Tropical incubation 16 The emulsion containing the mercury-gold amalgam dispersion showed no speed loss on incubation and had less fog increase than the control.

Example 6 A quantity of the mercury-gold amalgam of Example 2 was added to a negative-speed gelatino-silver bromoiodide emulsion at a concentration of 0.1 mg. of amalgam per mole of silver halide. The emulsion was coated on cellulose acetate film base and treated as in Example 4. The following results were obtained:

The emulsion containing the mercury-gold amalgam dispersion showed no speed loss on incubation and had less fog increase than the control.

Instead of incorporation in the silver halide emulsion, the fog inhibitors of my invention may be incorporated in a colloid layer such as a gelatin layer in contact with the emulsion side.

The mercury dispersions which we have described may be used in various kinds of photographic emulsions. In addition to being useful in ordinary non-sensitized emulsions, they may also be used in orthochromatic, panchromatic or X-ray emulsions. If used with sensitizing dyes they may be added to the emulsion before or after the dyes are added. Various silver salts may be used as the sensitive salt such as silver bromide, silver iodide, silver chloride or mixed silver halides. The mercury dispersions may be used in emulsions intended for color pho- 5 tography, for example, emulsions containing color-forming couplers or emulsions to be developed by solutions containing couplers. The dispersing agent for the silver halide or the mercury may be gelatin or other colloid such as collodion, albumin, cellulose derivatives or synthetic resins.

It will be understood that we contemplate as included within our invention all modifications and equivalents falling within the scope of the appended claims.

We claim:

l. A light-sensitive silver halide emulsion containing from .01 to 3 milligrams per mole of silver halide of elemental mercury selected from the class consisting of metallic mercury and mercury-gold amalgam, said elemental mercury being added to the emulsion in dispersion in a water-permeable colloidal medium.

2. A light-sensitive silver halide emulsion containing from .01 to 3 milligrams per mole of silver halide of metallic mercury added to the emulsion in dispersion in a water-permeable colloidal medium.

3. A light-sensitive silver halide emulsion containing from .01 to 3 milligrams per mole of silver halide of mercury-gold amalgam added to the emulsion in dispersion in a water-permeable colloidal medium.

4. A light-sensitive sulfur sensitized silver halide emulsion containing from .01 to 3 milligrams per mole of silver halide of elemental mercury selected from the class consisting of metallic mercury and mercury-gold amalgam, said elemental mercury being added to the emulsion in dispersion in a water-permeable colloidal medium.

5. A light-sensitive sulfur sensitized silver halide emulsion containing from .01 to 3 milligrams per mole of silver halide of metallic mercury added to the emulsion in dispersion in a water-permeable colloidal medium.

6. A light-sensitive sulfur sensitized silver halide emulsion containing from .01 to 3 milligrams per mole of silver halide of mercury-gold amalgam added to the emulsion in dispersion in a Water-permeable colloidal medium.

7. The emulsion of claim 4 which is additionally chemically sensitized with gold salts.

8. The emulsion of claim 4 which is additionally chemically sensitized with reduction sensitizers.

9. The emulsion of claim 4 which is additionally chemically sensitized with both gold salts and reduction sensitizers.

10. The method of reducing fog and loss of speed upon storage of a silver halide emulsion, which comprises incorporating in said emulsion at any stage prior to coating, a dispersion in a water-permeable colloidal medium of elemental mercury selected from the class consisting of metallic mercury and mercury-gold amalgam, said elemental mercury being present in an amount from .01 to 3 milligrams per mole of silver halide.

References Cited in the file of this patent UNITED STATES PATENTS 2,059,642 Kankelwitz Nov. 3, 1936 2,146,802 Dersch Feb. 14, 1939 FOREIGN PATENTS 533,110 Great Britain Feb. 6, 1941 OTHER REFERENCES Journal of the Optical Society of America, vol. 32, Apr. 1942, pages 219-223. (Copy in S. L.) 

1. A LIGHT-SENSITIVE SILVER HALIDE EMULSION CONTAINING FROM .01 TO 3 MILLIGRAMS PER MOLE OF SILVER HALIDE OF ELEMENTAL MERCURY SELECTED FROM THE CLASS CONSISTING OF METALLIC MERCURY AND MERCURY-GOLD AMALGAM, SAID ELEMENTAL MERCURY BEING ADDED TO THE EMULSION IN DISPERSION IN A WATER-PERMEABLE COLLOIDAL MEDIUM. 